Airbag supplemental restraint systems (SRS) have become increasingly pervasive because of their ability to protect vehicle occupants from serious injury in the event of a collision. A typical airbag system has an airbag, an inflation device, and a crash sensor that detects a sudden deceleration of the vehicle. In order to prevent accidental or unwanted airbag inflation, airbag systems generally require a high safety integrity level to prevent accidental or unwanted airbag inflation. One way to maintain a high safety integrity level is to use multiple sensors. For example, a typical side impact airbag system has a pressure sensor inside a car door, and an accelerometer located in a pillar next to the car door. If the pressure sensor measures a sudden rise in pressure at the same time the accelerometer detects an acceleration, the SRS system deploys the side impact airbag. By setting proper timing and amplitude conditions for the pressure sensor and accelerometer, the airbag is deployed in the event of a collision, but not from a vibration caused by a person closing the door, for example. Generally, the requisite sensing and triggering of the airbag system is coordinated by a microcontroller or microprocessor coupled to various elements of the SRS system.
One issue related to the safety integrity of SRS is the electrical integrity of the circuits and circuit boards that are coupled to the SRS system. This integrity is maintained, not only to the microcontroller and components of the SRS system, but also to the power supply system that provides power to the microcontroller and other elements of the SRS system.
For example, if there is a short circuit on a circuit board or other piece of electronic equipment that is associated with the SRS system, there is a possibility that the airbag may deploy under certain conditions when it should not. In another example, if power is removed from a circuit board or other piece of electronic equipment during an emergency situation, such as a collision, there is a possibility that the airbag may not deploy when it should. Thus, additional efforts are often necessary when designing electronic circuits for automotive safety applications. For example, automotive functional safety requirements may be specified in certain standards, such as ASEAL-D ISO26262.